Curable resin compositions, containing acryloyl group contained resin are widely used in the coating industry, for example as coating materials for paper, wood, metal and plastic, in printing inks, adhesives and sealants. Polymerization or crosslinking of acryloyl group contained resin compositions, also termed hereinafter as hardening or curing, is achieved by polymerization of acryloyl group containing, resins in the curable compositions in presence of radical initiators. Such initiators can be activated by UV (ultraviolet) irradiation or heat. Another option is the polymerization initiated by electron beam. In general, commercial production of resins, which contain acryloyl groups, is performed by esterification of oligomeric or polymeric multifunctional alcohols with an excess of acrylic acid. Such a process is described for example in comprehensive literature such as “Prepolymers and Reactive Diluents for UV- and EB-curable Formulations”, P. K. T. Oldring (Ed.), SITA Technologies, London, UK, 1991, page 124, 131. Despite widely used, this process is not entirely free of problems.
Acrylic acid is, as a rule, rather unstable at elevated reaction temperatures and carries the risk of spontaneous uncontrolled polymerization, if not properly inhibited.
The purification of acryloyl group containing resins from excess of acrylic acid and acidic catalyst is another problem, aggravated by high viscosity of the products. In the U.S. Pat. Nos. 5,945,489, 6,025,410 and WO specification 0100684, the inventors explain an appropriate route to make acryloyl group, which comes of acrylic ester, containing curable liquid compositions, which are prepared by Michael addition of β-dicarbonyl group containing compounds, e.g., acetoacetates and excess of multifunctional acrylate compounds. The use of acrylates, which are commercially available commodity products, such as trimethylolpropane triacrylate, the short reaction time, the low reaction temperature and the avoidance of acrylic acid and purification steps make this process particularly attractive as an alternative method to produce a curable liquid composition comprising a reactive acryloyl group contained resin.
However, the limitation of this process is that a very large excess of multifunctional acrylate compounds has to be used to avoid gellation during preparation and to provide liquid products having a useful viscosity. The excess of multifunctional acrylate compounds cannot be separated from the composition and remains as a reactive diluent. Therefore, most of the properties attributed to the final cured coating will be based on the cured properties of those multifunctional acrylate compounds. This is a limiting drawback, restricting product versatility and variety of product properties.
Moreover, use of large amounts of expensive multifunctional acrylate compounds also adversely affects raw material cost benefits in the mass production of such acrylated liquid compositions, as only low amounts of inexpensive β-dicarbonyl group containing (e.g., acetoacetylated) resins can be included.